The present invention relates to an electromagnetic optic element. More specifically the present invention relates to reflective multilayer x-ray optics having adjustable working wavelengths.
X-ray optics are used in many applications such as x-ray diffraction analysis and spectroscopy that require the directing, focusing, collimation, or monochromatizing of x-ray energy from an x-ray source. The family of x-ray optics or reflectors used in such applications presently include: total reflection mirrors having a reflective surface coated with gold, copper, nickel, platinum, and other similar elements; crystal diffraction elements such as graphite; and multilayer structures.
The reflective surfaces in the present invention are configured as multilayer or graded-d multilayer x-ray reflective surfaces. Multilayer structures only reflect x-ray radiation when Bragg""s equation is satisfied:
nxcex=2d sin(xcex8)
where
n=the order of reflection
xcex=wavelength of the incident radiation
d=layer-set spacing of a Bragg structure or the lattice spacing of a crystal
xcex8=angle of incidence
Multilayer or graded-d multilayer reflectors/mirrors are optics which utilize their inherent multilayer structure to reflect narrow band or monochromatic x-ray radiation. The multilayer structure of the present invention comprises light element layers of relatively low electron density alternating with heavy element layers of relatively high electron density, both of which define the d-spacing of the multilayer. The bandwidth of the reflected x-ray radiation can be customized by manipulating the optical and multilayer parameters of the reflector. The d spacing may be changed depthwise to control the bandpass of the multilayer mirror. The d-spacing of a multilayer mirror can also be tailored through lateral grading in such a way that the Bragg condition is satisfied at every point on a curved multilayer reflector.
Curved multilayer reflectors, including parabolic, elliptical, and other aspherically shaped reflectors must satisfy Bragg""s law to reflect a certain specific x-ray wavelength (also referred to as energy or frequency). Bragg""s law must be satisfied at every point on a curvature for a defined contour of such a reflecting mirror. Different reflecting surfaces require different d-spacing to reflect a specific x-ray wavelength. This means the d-spacing should be matched with the curvature of a reflector to satisfy Bragg""s law such that the desired x-ray wavelength will be reflected. Since Bragg""s law must be satisfied, the incident angle and d-spacing are normally fixed and thus the reflected or working wavelength is fixed.
The present invention is a multilayer x-ray reflector/mirror which may be used to reflect multiple x-ray wavelengths.
In a first embodiment, the multilayer structure has a laterally graded d-spacing. The working (reflected) wavelength of the multilayer reflector may be changed by simply varying its curvature and thus the angle of incidence for an x-ray beam to satisfy Bragg""s law.
In a second embodiment, an electromagnetic reflector has a fixed curvature and a multilayer structure that has been configured to include a plurality of distinct d-spacings. The multilayer structure has also been laterally graded such that the electromagnetic reflector may reflect multiple x-ray wavelengths according to Bragg""s law. Thus, the lateral grading of the d-spacings have been configured in conjunction with the curvature of the multilayer coating to reflect a plurality of x-ray wavelengths.
In a third embodiment of the present invention an electromagnetic reflector is formed with stripe-like multilayer coating sections. Each of the coating sections has a fixed curvature and graded d-spacing tailored to reflect a specific wavelength. To change the working wavelength of the reflector, the mirror or x-ray source need to be moved relative to each other so that the appropriate coating section is aligned with the x-ray source.